Debited incorrectly for months

Vodacom have over billed me for a couple months now <br> <br> Half way through the year there was a price increase of which notification was sent out <br> <br> But since then I believe another increase has been issued I didn't pick it up as I had not received any notification to another increase this is the only reasoning I can justify my current debit <br> <br> How can vodacom have to increases in lest than half a year <br> <br> I mailed vodacom my query and recieved no response <br> <br> I will close my account and go elsewhere if I am not reimbursed